A milking machine is commonly practice on medium to large dairy farms. The machine sucks the milk out of the teat by vacuum and includes a vacuum pump, a vacuum vessel, which also serves as a milk-collecting pail, a plurality of two or four teat cups connected by hoses to a manifold and a vacuum vessel, and a pulsator, which alternately applies vacuum and atmospheric pressure to the teat cups. The teat cup unit consists of a rigid outer case containing an inner elongated tube of elastomeric material (e.g., rubber), called the teat cup liner. The inside of the liner, in contact with the teat, is subjected to a constant vacuum of about 0.5 Bar during milking. The pressure in the pulsation chamber between the liner and teat cup is regularly alternated by the pulsator between 0.5 Bar during the suction phase and atmospheric pressure during the massage phase. The result is that milk is sucked from the teat cistern during the suction phase. During the massage phase the teat cup liner is pressed together to stop milk suction, allowing a period of teat massage and for new milk to run down into the teat cistern from the udder cistern. This is followed by another suction phase, and so on. Relaxation of the teat during the massage phase is necessary to avoid accumulation of blood and fluid in the teat, which is painful to the cow and will cause her to stop letting down. The pulsator alternates between the suction and massage phases 40 to 60 times a minute.
It is know in the art that the milking by means of a teat cup liner is provided in one stroke; The suction from the vacuum source is applied in a pulsating manner to both the inside of the liner, and to a space between the shell and the liner. A differential suction pressure between the inside and outside of the liner within the shell causes this portion of the liner, which is more flexible than adjacent portions, alternately to collapse and open up. When the liner opens up, the teat experiences a greater suction causing milk to flow. When the liner closes, the suction is released, and the liner closes around the end of the teat and presses inwards on the end of the teat. Certain problems have been noted in use with this type of teat cup liner. Firstly, the liner needs to be heavy enough to stretch the animal's teat to open milk ducts. The stretching of the teat stresses the teat tissue, the milk ducts, and sphincter valve at the end of the teat. It has hitherto been believed that this stretching is a cause of inflammation of the teat secretory tissues at the base of the animal's udder, and ultimately mastitis. It has also been thought that the sudden shut off of suction could cause milk to be sucked back into the teat, thereby causing or promoting mastitis. Apart from causing the animal discomfort and pain, these problems can shorten the animal's effective working life.
U.S. Pat. No. 6,427,624 to Briggs et al. discloses a teat cup liner for milking machine. U.S. Pat. No. 5,762,020 to van der Lely teaches an automatic milking apparatus often has a disadvantage in that, when during milking one of the cups is disengaged from a teat. Mastitis is basically an economical disease that rarely kills a cow; but it degenerates part of the udder, lowering milk production, and cost high medical and vet bills. The higher producing animals are more prone to this disease then others.
There is therefore a long need to modify the currant generation of vacuum pulsating milking machines in a way that milk will stream towards the milk tank and never get squirted back into the cow's udder.